suggestions for diagnosing a driveline shudder?

[dan juhasz]

I have a stock unmodified (has a 3:91 gear set) 67 hemi gtx 727 8 3/4 combination. Was out for an end of season cruise yesterday that included mostly highway speed driving. I generally stay between 55 and 60 because of the gears. Under part throttle at those speeds it is smooth as glass. If I lift at 60 to coast I felt a slight shudder. If I passed someone and say I lifted at 70 or above that shudder was much worse, back on the throttle shudder goes away immediately. I come home put it up on the lift checked for perhaps a u joint issue or even a pinion nut that may have loosened a bit. I don't feel and looseness or see any issue. I wouldn't suspect drive shaft balance to act this way. Last year I removed the tail shaft housing to stop a leak, I relaced the bushing which was wiped out and seal. Any ideas what I should look into next?

 

[MWbirdLOVER70]

I have a stock unmodified (has a 3:91 gear set) 67 hemi gtx 727 8 3/4 combination. Was out for an end of season cruise yesterday that included mostly highway speed driving. I generally stay between 55 and 60 because of the gears. Under part throttle at those speeds it is smooth as glass. If I lift at 60 to coast I felt a slight shudder. If I passed someone and say I lifted at 70 or above that shudder was much worse, back on the throttle shudder goes away immediately. I come home put it up on the lift checked for perhaps a u joint issue or even a pinion nut that may have loosened a bit. I don't feel and looseness or see any issue. I wouldn't suspect drive shaft balance to act this way. Last year I removed the tail shaft housing to stop a leak, I relaced the bushing which was wiped out and seal. Any ideas what I should look into next?

U joint sloppy? I had one acted fine then one day I heard a pop and busted tail shaft. U joint frozen

 

[davek]

do you feel it in the steering wheel or the shifter?

 

[Beekeeper]

tail shaft bushing worn? well I didn’t read enough I see you have replaced it so scratch that off the list

 

[NoCar2023]

Remove the propshaft and check u-joints for binding.

 

[dan juhasz]

do you feel it in the steering wheel or the shifter?

In the body not in the steering wheel

 

[dan juhasz]

Remove the propshaft and check u-joints for binding.

I’ll do that tomorrow

 

[dan juhasz]

Remove the propshaft and check u-joints for binding.

pulled the driveshaft and both u joints are perfectly smooth in their operation. Tail shaft bushing looks good too.

 

[NoCar2023]

What are your driveline angles?

 

[gtx6970]

I had a car many many years ago do this, After cking A LOT. thinking had to be U joint or pinion angle issues

It ended up being a collapsed trans mount isolator bushing

 

[dan juhasz]

What are your driveline angles?

honestly i don't know, everything stock so it didn't dawn on me to check for something like that

 

[bm02tj]

Also check your leaf springs

 

[Rishi]

In my experience, a shudder while decelerating is the U-joints. Even though you tested, it may still be U-joints, if you were feeling for play "by hand."

In contrast, a whining noise, when coasting on the highway and the car is decelerating slightly, is often the rear differential, the gears within not meshing perfectly, or a dry axle bearing. In any case, I would be surprised if your "shudder" issue relates to the rear differential, suspension, leaf springs, shocks, or wheels.

Another U-joint test:

Have a helper sitting in the running car, and with the parking and pedal (service) brakes firmly applied, shift the car into drive, then to neutral, then to reverse, then back to neutral, pausing for a few seconds at each stop. Repeat this a few times.

Meanwhile, during this shifting operation, look under the car and observe the drive-shaft for any play or movement. Ideally, the drive shaft does not move at all. Even in moderate mileage cars (200k-ish, 50+ year old equipment) things remain pretty tight, when the parking and service brake are firmly applied.

Another point to observe is movement between the front yoke (at the transmission tail housing) and the drive shaft during this test. Also, the rear yoke (at the differential) and the drive shaft. If there is any movement between these components, you may have a U-joint wearing out.

Some of the U-joints I've seen over the years have NO grease zerk fitting, and it seems possible the grease within can dry and lubrication is diminished, thereby increasing wear to the needle bearings of the U-joint.